We studied the prognostic value of the enzymes acid alpha-naphthyl acetate esterase (ANAE) and acid phosphatase (AP) in 89 children with acute lymphoblastic leukemia (ALL). Follow-up data were available for 61 out of 67 cases of non T- non B-ALL, which were treated in different hospitals according to the same protocols. Sex, age, initial white blood cell count (WBC) and number of high risk patients (WBC above 25 X 10(9)/l) were comparable between enzyme-positive and -negative cases. The probabilities of complete continuous remission (CCR) were virtually identical in the AP+ and AP- group. For the ANAE+ group the probability of CCR was lower than for the ANAE- group, but this difference was not statistically significant (0.10 greater than p greater than 0.05). Within the common-ALL group (n = 32), no difference was found in probability of CCR between the AP+ and AP- group but ANAE+ cases had a significantly lower probability of CCR than ANAE- cases. This study is a contribution to the view that the cytochemical profile of ALL cells may have prognostic value.